Process for producing a quadrupole electrode arrangement

ABSTRACT

The invention relates to a quadrupole electrode arrangement comprising two shaped parts (10, 11). Each shaped part (10, 11) is produced from an insulating plate-shaped carrier (2) and a metal blank (1) fastened thereto. Each two of the four opposing electrode surfaces (4.1-4.4) are, for example, milled, turned and ground from the metal blank. Each shaped part (10, 11) also has a ground connection surface (6.1, 6.2) which defines the distance of the quadrupole electrode pairs precisely when the two structural parts are joined.

TECHNICAL FIELD

The invention relates to a process for producing a quadrupole electrodearrangement and to a quadrupole electrode arrangement and a massspectrometer.

STATE OF THE ART

Mass spectrometers are known in a variety of designs and are used forthe analysis of chemical structures (cf e.g. U.S. Pat. No. 5,389,785,U.S. Pat. No. 5,298,745, U.S. Pat. No. 4,949,047, U.S. Pat. No.4,885,470, U.S. Pat. No. 4,158,771 or U.S. Pat. No. 3,757,115). Inprinciple, such instruments have an ion source, one (or more) ionfilters and an ion detector. The gaseous ions are selected by the ionfilter, which is typically formed of a quadrupole electrode arrangementwith hyperbolically shaped surfaces. It is important for the hyperbolicsurfaces to be made with very high precision and to be the rightdistance apart. In particular, precise positioning of the electrodesurfaces has presented considerable difficulties hitherto.

DESCRIPTION OF THE INVENTION

The object of the invention is to provide a process for producingquadrupole electrode arrangements for mass spectrometers and the likewhich affords a high precision of the electrode arrangement whileincurring the lowest possible expenditure on assembly.

The solution according to the invention is defined by the features ofclaim 1. The quadrupole is thus produced essentially from two shapedparts, each of which has two electrode surfaces machined out of it andat least one coupling surface. The two parts are shaped so that they canbe placed directly against one another and joined together via thecoupling surfaces. In the joined state, the two electrode pairs areexactly the right distance apart. The invention makes use, inter alia,of the fact that an individual shaped part can be produced with veryhigh precision, e.g. by turning, milling and/or grinding. Machining twoelectrode surfaces out of one shaped part ensures that at least thesetwo electrode surfaces are the right distance apart.

In a preferred embodiment, the two shaped parts are formed essentiallyof a plate-shaped carrier and a shaped block fixed thereto. The carrieris made of an insulating material, e.g. glass, and the block is madee.g. of a conducting material, for example stainless steel or aluminum.In the manufacturing process according to the invention, the block isfixed to the carrier in the raw state (i.e. as a blank) and thenmachined. Accordingly, for example, half of the quadrupole interiorchamber is hollowed out of a steel plate by turning so that the interiorchamber of the quadrupole electrode arrangement is created when the twoparts are joined together. Feed lines can also be attached to the steelplate for evacuation of the interior chamber. The important aspect isthat two electrode surfaces and a coupling surface can be produced in asingle chucking.

Instead of a metal plate, it is also possible to use a ceramic plate;after the electrode surfaces have been shaped, this is selectivelyprovided with a conducting layer (of copper, gold, platinum etc.).

The two shaped parts are advantageously formed with mirror symmetry. Theprocess is particularly suitable for producing ion filters curved in theshape of a circular arc. Precision lathes are particularly good atproducing circular shapes. However, the invention is also advantageousin the case of linear electrode arrangements.

So that two disk-shaped parts can be joined together with precision,each one is provided e.g. with a central bore. The two carriers can bemutually aligned with an expanding arbor.

With a quadrupole electrode arrangement produced according to theinvention, it is also easy to seal the interior chamber between theelectrodes so that the required high vacuum can subsequently be created.It is also possible to mill radial slots in the plates, into which ionlenses can be inserted at a later stage.

A mass spectrometer according to the invention comprises an ion source,a quadrupole electrode arrangement with electrodes curved in the shapeof a circular arc, and a detector. There is also a vacuum pump forevacuation of the quadrupole interior chamber. Preferably, this is atleast partially built into the double plate arrangement. In aparticularly preferred embodiment, the double plate arrangement hasseveral sectors separated by ion lenses. One of these can be filled witha gas to act as a collision cell (for breaking the incoming ions downinto several individually analyzable components).

Further advantageous embodiments and combinations of features can befound in the following detailed description and in the claims taken as awhole.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings used to illustrate the Examples:

FIGS. 1a-c are a schematic representation of the steps of themanufacturing process;

FIG. 2 is a schematic perspective of two shaped parts which can bejoined together;

FIG. 3 is a schematic representation of a circular quadrupole electrodearrangement in section.

In the drawings, identical parts always carry identical referencenumbers.

MODES OF CARRYING OUT THE INVENTION

FIGS. 1a-c illustrate the essential steps of the process according tothe invention. In FIG. 1a, a metal plate 1 (e.g. made of steel oraluminum) is first glued and/or screwed to a carrier 2 made of aninsulating material (e.g. glass). The metal plate 1 and the carrier 2are e.g. disk-shaped. They may have the same diameter, but this is notobligatory. The dimensions of the metal plate 1 depend on the quadrupoleelectrode arrangement to be produced. The thickness is e.g. in theregion of 1 cm and the diameter is in the region of 5-50 cm, especially10-30 cm.

The blank shown in FIG. 1a is clamped in the chuck 3.1, 3.2 of adigitally controlled milling machine (FIG. 1b). The desired electrodesurfaces 4.1-4.4 are then machined out of said blank. In the sectionalrepresentation shown in FIG. 1b, they have a hyperbolic shape. Theelectrode surfaces 4.1-4.4 are moreover designed in the shape of acircular arc in a plane perpendicular to the plane of the drawing. Inthis Example, the electrode surfaces 4.1, 4.2 on the one hand and 4.3,4.4 on the other belong to two different ion filters connected to oneanother in series, but it is perfectly conceivable in a differentembodiment for the electrode surfaces 4.1, 4.4 and 4.2, 4.3 toconstitute a single continuous surface. In this case the ion filterwould form a circular arc of more than 180°.

A coupling surface 6.1 is ground in the central region inside theelectrode surfaces 4.2 and 4.3. Said coupling surface must beelectrically separated from the electrode surfaces 4.2, 4.3 by anannular insulating region 5. In the insulating region 5 and between theelectrode surfaces 4.1 and 4.2 and, respectively, 4.3 and 4.4, the metalplate 1 is milled right down to the carrier 2. For this reason the metalplate 1 and the carrier 2 must if possible be bonded together over theirwhole area or at specific points so that individual parts of the metalplate cannot fall off the carrier on milling.

A central bore 7 and several bores 8.1, 8.2 are also made; these passright through both the metal plate 1 and the carrier 2. They aresubsequently used to join two shaped parts together, as shown in FIG.1c. An expanding arbor 9 is inserted into the central bore 7. It alignsthe two shaped parts 10, 11, which essentially have mirror symmetry (andare produced by the process shown in FIGS. 1a, b).

The mutual distance between the electrode surfaces 4.1, 4.2 and 4.5, 4.6etc. is determined by the high-precision grinding of the joined couplingsurfaces 6.1, 6.2 of the two shaped parts 10, 11, ensuring that there isan insulating gap between opposing electrode surfaces 4.1, 4.5 and 4.2,4.6. Contact over the whole area of the coupling surfaces 6.1, 6.2 isprovided by the clamping screws 12.1, 12.2.

The Example which has now been described is distinguished in particularby the following advantages:

a) Several electrode surfaces are formed on a single shaped part and canbe machined in one chucking. All the shapes which can be machined withinone chucking can be produced with very high precision, accuratelydetermining the geometric distances between the different surfaces.

b) Any unevennesses between the metal plate (1) and the carrier (2) canbe compensated by applying glue.

c) The quadrupole electrode arrangement is produced by joining togetheronly two shaped parts machined by the same process. Inaccuracies due toassembly can be reduced to a minimum.

d) In principle, the quadrupole interior chamber is already fairlyaccurately defined by a single shaped part because it is determinedrelative to the coupling surface 6.1 by the V-shaped recess between theelectrode surfaces 4.1, 4.2. Each of the two shaped parts 10, 11, withmirror symmetry, forms or contains half of the quadrupole interiorchamber. In this way, said chamber is much more accurately defined thanin the state of the art.

e) Because only two shaped parts (and not a large number as in the stateof the art) have to be joined together, the expenditure on assembly iscomparatively low. Exact positioning is assured by the expanding arbor.A further gain in terms of accuracy is derived from the fact that theshaped parts are joined to one another directly and not via anadditional fixing member.

f) The quadrupole electrode arrangement is easily scalable. In otherwords, the milling data can be calculated by computer, scaled to thedesired size and then executed by a CNC machine. If, for example, anelectrode arrangement of larger radius of curvature is required, it isonly necessary to calculate and transfer the new milling data and clampa blank of appropriate size in the chuck. As regards assembly, on theother hand, nothing needs to be changed.

g) In the case of a revision, the double plate construction can beseparated into the two shaped parts without excessive expenditure.

As shown in FIG. 2, three sectors 13, 14, 15, separated by slots 16, 17,can be formed on the shaped parts 10, 11. Each of these sectors 13, 14,15 forms an ion filter and filters the ions coming into the quadrupolearrangement. Apertures can be inserted into the slots 16, 17 in theradial direction so that the ion beam is focused better on the inletside of the next sector. The sectors 13, 14, 15 occupy only about 3/4 ofthe circular arc. The remaining quarter is a free sector 18 (for theinput and output of the ion beam).

In a particularly preferred embodiment, the middle sector 14 is designedas a collision cell, i.e. this sector 14 is separated from the othersand filled with an inert gas.

The functional design of a mass spectrometer (including collision cell)is known from the state of the art and does not require furtherexplanation here. FIG. 3 shows an embodiment with integrated vacuumsystem. It is known that the quadrupole interior chamber 24 must beevacuated in operation. Instead of placing the entire quadrupoleelectrode arrangement in an evacuated volume, specific sealed interiorchambers between the shaped parts can be selectively connected to anultrahigh vacuum pump.

FIG. 3 shows a cutout of the construction according to the invention,comprising two carrier plates 19.1, 19.2 with the various parts betweenthem. The outermost parts (relative to the central axis 31 of thecarrier plates 19.1, 19.2, shown on the right in FIG. 3) are two spacers21.1, 21.2 with a seal 22 between them. The electrodes 23.1-23.4, whichare further in along the radius, are thus located in a volume(insulating region 26, 27 and quadrupole interior chamber 24) which isgastight to the outside. Said volume can be pumped out via a pluralityof radial channels 29 in the spacers 25.1, 25.2. The radial channels 29are connected e.g. to a large slot-shaped opening 28 running through thecarrier plates 19.1, 19.2 in the direction of the central axis 31.

In this Example, the spacers 21.1, 21.2, 25.1, 25.2 and the electrodes23.1-23.4 are rigidly joined to the carrier plates 19.1, 19.2 by screws20.1-20.6. In the central region between the carrier plates 19.1, 19.2,provision can be made for an empty space 30 into which the electronicsfor controlling the quadrupole electrode arrangement can be integrated.The electric cables between this control switch and the electrodes23.1-23.4 can be brought out parallel to the screws 20.2, 20.3, 20.5,20.6, through the carrier plates 19.1 and 19.2, and connected to theswitch from there.

It is understood that the individual features of the different Examplescan be combined in a very wide variety of ways. Accordingly it ispossible to meet a very wide variety of user requirements.

In summary, it should be emphasized that the invention has provided amanufacturing process which allows high-precision positioning of theelectrodes with minimal expenditure on assembly. In economic terms, thisalso reduces the production costs. The devices produced in this way arevery compact and facilitate the mobile use of mass spectrometers.

What is claimed is:
 1. Process for producing a quadrupole electrodearrangement comprising two shaped parts (10, 11), each of which has twoelectrode surfaces (4.1, 4.2; 4.3, 4.4) machined out of it and at leastone coupling surface (6.1, 6.2), so that, when the shaped parts (10, 11)are joined together at the coupling surfaces (6.1, 6.2), the electrodesurfaces (4.1-4.4) delimit a desired quadrupole interior chamber (24),characterized in that the two shaped parts (10, 11) are produced from aplate-shaped carrier (2) made of an insulating material and a metalblank (1) attached thereto.
 2. The process according to claim 1,characterized in that the two shaped parts (10, 11) are formedessentially with mirror symmetry.
 3. The process according to one ofclaim 1 or 2, characterized in that the carrier (2) is made of glass andthe blank (1) is made of steel.
 4. The process according to claim 3,characterized in that the two shaped parts (10, 11) are produced fromdisk-shaped plates and are provided with a central bore (7) so that theycan be joined together in alignment.
 5. The process according to claim 1or 2, characterized in that the two shaped parts (10, 11) are producedfrom disk-shaped plates and are provided with a central bore (7) so thatthey can be joined together in alignment.
 6. A quadrupole electrodearrangement, especially for mass spectrography, constructed from twoplate-like shaped parts (10, 11), each of which has two electrodesurfaces (4.1, 4.2; 4.3, 4.4) machined out of it and which are joinedtogether via coupling surfaces (6.1, 6.2) in such a way that theelectrode surfaces (4.1-4.4) delimit the desired quadrupole interiorchamber, characterized in that the two shaped parts (10, 11) areproduced from a carrier (2) made of an insulating material and a metalblank (1), out of which the electrode surfaces are machined.
 7. Theqaudrupole electrode arrangement according to claim 6, characterized inthat the shaped parts (19.1, 19.2), joined together, enclose avacuum-tight interior chamber (24, 26, 27) which can be pumped out viachannels (28, 29) provided in the shaped parts (19.1, 19.2).
 8. Theqaudrupole electrode arrangement according to claim 6 or 7,characterized in that an empty space (30) is provided in the shapedparts (19.1, 19.2) for a control switch.
 9. The quadrupole electrodearrangement according to claim 8, characterized in that the shaped partsform several sectors in the shape of a circular arc, with radial slotsbetween them.
 10. A mass spectrometer with a quadrupole electrodearrangement according to claim
 8. 11. The quadrupole electrodearrangement according to claim 6 or 7 characterized in that the shapedparts form several sectors in the shape of a circular arc, with radialslots between them.
 12. A mass spectrometer with a quadrupole electrodearrangement according to claim
 11. 13. A mass spectrometer with aquadrupole electrode arrangement according to claim 6 or 7.